Journal of Oceanography

, Volume 63, Issue 2, pp 293–307 | Cite as

Temporal variability of winter mixed layer in the mid-to high-latitude North Pacific

  • Eitarou Oka
  • Lynne D. Talley
  • Toshio Suga
Original Papers


Temperature and salinity data from 2001 through 2005 from Argo profiling floats have been analyzed to examine the time evolution of the mixed layer depth (MLD) and density in the late fall to early spring in mid to high latitudes of the North Pacific. To examine MLD variations on various time scales from several days to seasonal, relatively small criteria (0.03 kg m−3 in density and 0.2°C in temperature) are used to determine MLD. Our analysis emphasizes that maximum MLD in some regions occurs much earlier than expected. We also observe systematic differences in timing between maximum mixed layer depth and density. Specifically, in the formation regions of the Subtropical and Central Mode Waters and in the Bering Sea, where the winter mixed layer is deep, MLD reaches its maximum in late winter (February and March), as expected. In the eastern subarctic North Pacific, however, the shallow, strong, permanent halocline prevents the mixed layer from deepening after early January, resulting in a range of timings of maximum MLD between January and April. In the southern subtropics from 20° to 30°N, where the winter mixed layer is relatively shallow, MLD reaches a maximum even earlier in December–January. In each region, MLD fluctuates on short time scales as it increases from late fall through early winter. Corresponding to this short-term variation, maximum MLD almost always occurs 0 to 100 days earlier than maximum mixed layer density in all regions.


Winter mixed layer North Pacific temporal variability Argo 


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Copyright information

© The Oceanographic Society of Japan/TERRAPUB/Springer 2007

Authors and Affiliations

  1. 1.Institute of Observational Research for Global ChangeJapan Agency for Marine-Earth Science and TechnologyYokosuka, KanagawaJapan
  2. 2.Scripps Institution of OceanographyUniversity of CaliforniaSan Diego, La JollaU.S.A.
  3. 3.Department of Geophysics, Graduate School of ScienceTohoku UniversityAoba-ku, SendaiJapan
  4. 4.Ocean Research InstituteThe University of TokyoNakano-ku, TokyoJapan

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